The present invention relates to optical analysis systems and methods for analyzing fluids and, in particular, systems and methods for analyzing a flow of a fluid at two or more discrete locations to determine a characteristic of a substance in the fluid.
In the oil and gas industry, several flow assurance techniques are employed to monitor the formation of both organic and inorganic deposits in flowlines and pipelines. These deposits can seriously impede the productivity of wells by reducing the near wellbore permeability of producing formations and progressively restrict the diameter of the connected flow conduits, flowlines and pipelines. Problems relating to flow assurances cost the oil industry billions of dollars worldwide for prevention and remediation.
Flow assurance problems are most often related to paraffin waxes and asphaltenes, which are typically caused by changes in the pressure and temperature of the produced fluids at or near the wellbore or in surface flow conduits. As the waxes and asphaltenes precipitate out of the fluid, the precipitates can accumulate and tend to restrict or clog flowlines and pipelines. Removing the precipitates can be done using solvent washes, although, in some cases, the disposal of certain solvents after cleaning presents increasing environmental concerns. In other applications, the precipitates are removed by pipeline grinding, scraping or pigging operations undertaken by an inline tool/device/robot. In extreme cases, this may require that the flowline or pipeline be shut down for a period of time and, in the case of a total blockage, can even require removal of the entire pipeline altogether.
Calcium carbonate scale is usually formed by changes in the pressure and temperature of produced water at or near the wellbore and within the production tubing/flow conduits. Barium, strontium and calcium sulfate scales are usually formed by the mixing of different formation water and also the mixing of formation water and seawater that is injected into producing wells. Scale formation may be partly prevented by water shut-off treatments and the use of scale inhibitors. Once formed, scale can be removed only with some difficulty, such as by dissolving the scale, where applicable, using mineral acids and specially-designed dissolvers. In extreme cases, the scale must be removed by either inline milling operations or removing and replacing the affected flowline or pipeline altogether.
Hydrates lattice compounds of methane and water are crystals which, if formed, may also foul or block flowlines and pipelines. Aromatics and naphthanates when combined with water can cause the formation of foam and/or emulsions that may also cause flow restriction or pipeline interruption. Reservoir erosion can also adversely affect production by adding particulates to the stream and altering subsurface flow characteristics.
Those skilled in the art will readily recognize the importance in accurately determining the effectiveness of treatments designed to counteract asphaltenes, wax, scale, corrosion, as well as monitoring sand/chalk loss, all of which can adversely affect hydrocarbon production. In some cases, production of a well from a particular reservoir can be permanently damaged by flow problems making prevention essential to proper reservoir management. Accordingly, identifying flow assurance issues before they occur will mitigate costly corrective action.